Abstract

Frog tadpoles, injected with prolactin or somatotrophin during early stages when the brain cell population is rapidly increasing, exhibited marked increases over sham-injected controls in body weight, brain weight, and brain DNA, throughout subsequent development. Animals treated with somatotrophin attained the increase in brain DNA during the infection period. Prolactin had little effect during this period, but brain DNA accumulation continued at an accelerated rate over the next 15 days, when the rate of DNA increment normally declined. Patterns of incorporation of tritiated thymidine confirmed that both hormones increased DNA accumulation, suggesting increased cell proliferation rather than decreased cell death.